Kate, in her role as Royal Patron of East Anglia's Children's Hospices, was in Norfolk - close to their Anmer Hall home - to officially open The Nook children's hospice.
The lace gown was designed by Alexander McQueen and is a very different look to what the future Queen of England usually wears. For Friday's appearance the Duchess paired her two-piece suit with black tights, a clutch, and black pumps.
Britain's royal family has attended the Royal Variety Performance since 1912, the year it started.
The Duchess of Cambridge is determined to lose her "gatekeeper" after lawful two years - however the pair are talked about to be parting on the "handiest of terms". Prince George, six, Princess Charlotte, four, and Prince Louis, one, were never far from their parents' minds during their night out, and were brought up in conversation on several occasions.
The Cambridges smiled and waved to fans on arrival, and met with performers before and after the show, including the cast of the new Mary Poppins musical.
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Yakuza 0, Yakuza Kiwami 1, and Yakuza Kiwami 2 are all coming to Xbox One , and will be available on Game Pass in "early 2020". On PC you'll get the chance to scratch your strategy itch with Age of Empires II Definitive Edition and Hearts of Iron IV .
The evening is being hosted by comedians Rob Beckett and Romesh Ranganathan.
The Duke and Duchess will also hear performances from Lewis Capaldi, Mabel, Robbie Williams, the cast of Come From Away, and a collaboration by Emeli Sandé and Manchester's Bee Vocal choir.
Ahead of the event, the Kensington Palace Instagram page shared a "throwback" photo of Her Majesty attending the event in 1952 with Prince Philip and Princess Margaret.
In July 1919, the second Royal show was performed and was the first to be billed a 'Royal Variety Performance, ' before becoming an annual event in 1921.
The Royal Variety Performance is created to raise money for the Royal Variety Charity, which was formerly known as The Entertainment Artistes' Benevolent Fund.